i too had the problem,galaxy note 3 n9005 while connecting via usb shows unable to connect devices via usb 3.0.i tried everything changing cable,pcs,removed memory card,factory reset my phone,reinstalled many drivers,but nothing worked out.
SOLUTION:- I just plugged another note 3 n9005 into my pc,but it supported usb 3.0 and auto installed a driver.then i plugged my note 3,it worked like charm....try it